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Lexing, parsing, pretty-printing, and metaprogramming facilities for dealing with GraphQL schemas and queries
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dmjio/graphql-meta
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AGraphQL toolkit providing the following:
- AlexLexer of the
GraphQLlexical specification. - HappyParser of the
GraphQLBNF Grammar. - Pretty printer of the
GraphQLabstract syntax tree (AST) for human consumption. - QuickCheck generators for creating random AST fragments
- Used in conjunction with pretty printing to establish round trip property tests.
- Source
- Generics implementation providing correct-by-construction
Schemaat compile time. - QuasiQuoter providing inline definitions of
ExecutableDefinitions.
{-#LANGUAGE QuasiQuotes #-}moduleMain (main)whereimportGraphQL.QQ (query)main::IO()main=print [query| { building (id: 123) {floorCount, id}} |]QueryDocument {getDefinitions= [DefinitionOperation (AnonymousQuery [SelectionField (FieldNothing (Name {unName="building"}) [Argument (Name {unName="id"}) (ValueInt123)][] [SelectionField (FieldNothing (Name {unName="floorCount"})[][][]) ,SelectionField (FieldNothing (Name {unName="id"})[][][]) ])]) ]}
GraphQLExecutableDefinition abstract syntax tree rewriting is made possible via Template Haskell's metavariable substitution. DuringQuasiQuotation all unbound variables in aGraphQL query that have identical names inside the current scope will automatically be translated intoGraphQL AST terms and substituted.
buildingQuery::Int->ExecutableDefinitionbuildingQuery buildingId= [query| { building (id: $buildingId) {floorCount, id}} |]
QueryDocument {getDefinitions= [DefinitionOperation (AnonymousQuery [SelectionField (FieldNothing (Name {unName="building"}) [Argument (Name {unName="buildingId"}) (ValueInt4)][] [SelectionField (FieldNothing (Name {unName="floorCount"})[][][]) ,SelectionField (FieldNothing (Name {unName="id"})[][][]) ])]) ]}
It is possible to derive GraphQL schema usingGHC.Generics.Simply importGHC.Generics, deriveGeneric (must enable theDeriveGeneric language extension) and make an instance ofToObjectTypeDefintion.See below for an example:
{-#LANGUAGE DeriveGeneric #-}moduleMainwhereimportGHC.Generics (Generic)importGraphQL.Internal.Syntax.Encoder (schemaDocument)importData.Proxy (Proxy)importqualifiedData.Text.IOasTimportGraphQL.Generic (ToObjectTypeDefinition(..))dataPerson=Person{name::String ,age::Int}deriving (Show,Eq,Generic)instanceToObjectTypeDefinitionPersonshowPersonSchema::IO()showPersonSchema=print$ toObjectTypeDefinition (Proxy@Person)-- type Person{name:String!,age:Int!}- Generic deriving is currently only supported on product types with record field selectors.
- Only
ObjectTypeDefintionis currently supported.
- Generic deriving of
ScalarTypeDefintionandEnumTypeDefintion.
- Inspired by@edsko's workQuasi-quoting DSLs for free.
AlexandHappylexing & parsing inspired byconfig-value
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